public class Postgraduate extends Student {
    private String researchField;

    public Postgraduate(String name, int age, String researchField) {
        super(name, age);
        this.researchField = researchField;
    }

    public String getResearchField() {
        return researchField;
    }

    public void setResearchField(String researchField) {
        this.researchField = researchField;
    }

    @Override
    public String toString() {
        return "Postgraduate{" +
                "researchField='" + researchField + "'," +
                super.toString() +
                "}";
    }

    public void introduce() {
        System.out.println("Hello, I am a postgraduate student studying " + researchField);
    }

    public void study() {
        System.out.println("Studying advanced topics in " + researchField);
    }
}